Elon Musk has "cured" astrophysicist Neil deGrasse Tyson of his urges to drive a flying car.

On Sunday's episode of his "StarTalk" radio show, Tyson sat down with the CEO of SpaceX and Tesla Motors to discuss a variety of topics, ranging from Musk's fear of artificial super intelligence to the colonization of Mars. Musk also dumped a bucket of ice-cold reality on Tyson's dream of driving a flying car someday.

"If there are flying cars, then well obviously you have added this additional dimension where a car could potentially fall on your head and would be susceptible to weather," Musk said. "And of course you'd have to have a flying car [that operates by] autopilot because otherwise, forget it."

Think weaving through traffic on a busy day is frustrating? Try adding an entirely new dimension to the mix. "Essentially with a flying car you're talking about going 3-D," Musk says. "There's a fundamental flaw with cities where you've got dense office buildings and apartment buildings and duplexes, and they're operating on three dimensions, but then you go to the street, and suddenly they're two-dimensional."

Getting your 3-D driving license from the DMV isn't the only challenge a future of flying cars would have to overcome, Musk added. While Tesla has announced an update that promises to ease drivers' "range anxiety," seeing a flashing empty light while your car is in midair might cause more of a range heart attack. And just imagine being one of the poor street-bound souls if two-ton automobiles start falling out of the sky.

"Even in autopilot, and even if you've got redundant motors and blades, you've still gone from near-zero chance of something falling on your head to something greater than that," Musk said.

Also, if you want something as heavy as a car to fly, you've got to expect some noise, Musk explained. The closest things we have to a flying car today are helicopters. If your image of the future includes picturesque midair lanes filled with layers of silent cars whizzing by, you might need to recalibrate it.

Instead, Musk said, he imagines a much more viable alternative would involve digging into the earth and effectively creating subway tunnels for cars.

"If you were to extrapolate that to cars and have more car tunnels, then you would alleviate congestion completely," he said. "You would not need a flying car in that case, and it would always work even if the weather was bad. It would never ice up and it would never fall on your head."